1. Field of the Invention
This invention relates to an optical apparatus consisting of an optical unit comprising a plurality of optical elements wherein the adjustment of a certain optical element affects the results of adjustment of the other optical elements along with an adjustment apparatus that adjusts the optical elements, the adjustment method therefor, and a storage medium recorded with a processing program that executes said adjustment method, and also relates to lasers, wave-front controllers or telescopes as the optical apparatus that use said adjusted optical units.
2. Description of the Prior Art
Conventional methods of raising the performance of functions implemented by optical apparatus to a stipulated target value include (1) having the optical elements be adjusted by a skilled technician and (2) adopting high-precision optical elements.
However, with the method (1) of having the optical elements be adjusted by a skilled technician, it is necessary to perform the adjustments at the place where the optical apparatus is installed, and when one optical element is adjusted, it becomes necessary to adjust the other optical elements associated with that element, and thus a large amount of time is needed for the adjustment. In addition, adequate adjustment results may not be obtained even with a skilled technician, and it is not possible to make an objective judgment as to whether or not the results of adjustment of the optical apparatus are suitable. Moreover, there is also the problem of high adjustment costs due to the need for a skilled technician.
In order to minimize the burden of adjustment of optical elements by skilled technicians, the method (2) of adopting high-precision optical elements has been used. However, high-precision optical elements have problems in that they are typically expensive and a stable supply is not available, thus complicating the manufacture of optical apparatus.
For this reason, the conventional methods had drawbacks in that the manufacturing costs for optical apparatus were high, adjustment by skilled technicians was necessary and adjustment times were long.
In the aforementioned adjustment methods, were automatic adjustment to be possible, then this would be effective since skilled technicians would not be necessary. However, in the adjustment of adjustment location (1), as shown in FIG. 2, typically the effects of the adjustment location on the functions of the optical apparatus are not independent of other adjustment locations, so automatic adjustment is extremely difficult, and thus a skilled technician has been required for this adjustment.
To wit, in the case in which an optical apparatus has a plurality of adjustment locations, it is often the case that there are mutual dependencies between these adjustment locations. FIG. 2 is an explanatory diagram showing an example of a case in which there are dependencies (correlations) between the adjustment location and adjustment results across adjustment locations. For example, the first adjustment location may be adjusted to optimize the functions of the optical apparatus and then the second adjustment location is adjusted further to optimize the functions of the optical apparatus. At this time, since the adjustment of the second adjustment location was performed, the results of adjusting the first adjustment location are no longer optimized, and if readjustment is performed, results of adjustment different from the first time would be optimal.
We shall now explain these dependencies using the laser cavity as an example. The laser cavity typically consists of three or more mirrors and prisms, and the light path is a loop. Here, changing the position or orientation of one mirror changes the entire light path. Thus this also changes the optimal position and orientation of all of the mirrors. This means that changing either the position or direction of a mirror or prism, which are the adjustment locations, will change the optimal results of adjustment of all of the other adjustment locations.
In the case in which the adjustment of a plurality of adjustment locations are not independent as described above, the magnitude of the range of adjustment has the same number of dimensions as the number of interconnected adjustment locations, so the adjustment search space expands exponentially with the number of adjustment locations, leading to a combinatorial explosion and thus adjustment requires an unrealistic amount of time, or adjustment may become impossible. As one example, if we assume that there are 10 adjustment locations that are adjusted with an 8-bit setting signal, considering the case in which all are associated, the adjustment search space includes an enormous number of combinations calculated to be 2880≈1024 (10 to the power of 24), so adjustment by conventional methods requires an unrealistic amount of time and is thus impossible.
Conventional industrial laser apparatus consists of mirrors, laser crystals (optical crystals), dispersion elements (prisms) and other optical components and support components. In a laser cavity consisting of these components, the layout of the optical components must be set with micrometer accuracy. Mirrors must be adjusted in five different directions: longitudinal, lateral, vertical, lateral reflection angle and vertical reflection angle. Two or more mirrors and their support components are installed within a laser oscillator. When functional improvements are made to a laser apparatus such as increasing its power or shortening its pulse, the number of mirrors, dispersion elements or other optical components can reach six or more. The number of adjustment locations on their support components can become large at 30 or more locations.
On the other hand, since the intensity of light is strong in the laser cavity, nonlinear phenomena are induced due to the Kerr-lens effect, so the laser output light is subject to fluctuations in its power, wavelength, lateral modes and the like. Therefore, the optimal layout conditions for the optical components also change depending on the nonlinear phenomena. In the case of a pulsed laser, the optimal layout of the optical components differs between the shortest-pulse conditions and the maximum-output conditions.
The search for optimal layout conditions is typically performed by a skilled engineer. In the case in which the number of optical components is roughly six, this generally takes a skilled person roughly one week but an unskilled person would require adjustment time of one month or more. Moreover, in the aforementioned adjustment, since the positions of the support components for optical component slip with time, the light output of a laser apparatus fluctuates with time so the adjustment becomes even more difficult.
The optimization of a laser apparatus is conventionally performed through feedback to the laser apparatus of information on the light output from the laser apparatus. This information on the light output consists of the power (intensity of the light output), position and direction of the light path, wavelength, phase, wave front, pulse width and the like. When the laser beam is spatially divided and this information is evaluated for each, a large number of evaluation values are obtained. These evaluation values are mutually dependent and these correlations depend on the operating conditions of the laser apparatus. It is quite typical for two or more evaluation values to be present in this manner.
However, in the prior art, regarding power among the information on the light output, only the excitation light intensity is subjected to control, and regarding the position and direction of the light path among the information on the light output, only the position/direction of the mirrors whose position/direction is controllable are subjected to control.
These methods are characterized by finding a single optical element that strongly affects the evaluation values and then performing feedback control on that single element. In these methods, only a single element is optimized so the entire laser apparatus is not optimized.
Furthermore, there are many cases wherein these evaluation values have a strongly nonlinear correlation, and in these cases, there are problems wherein the optimization of the adjustment locations over the entire optical apparatus becomes difficult and the efficiency of optimization becomes extremely poor.
In a wave-front controller, precisely calculating the value of the phase at each point in the wave front would take an impractical length of time, so it is difficult to achieve good characteristics in the functions of a wave-front controller.
In a telescope, when the object to be observed is imaged on the image plane using a large concave mirror, the position/shape of the reflecting surfaces of the concave mirror diverge from the ideal position/shape, so the resolution of the image drops.
In addition, optical apparatus has problems in that vibration and shock during movement or transportation changes the layout of the constituent elements, causing deterioration in the performance of the apparatus.
In this manner, optical apparatus requires an overall adjustment of the position, direction, optical characteristics and such (hereinafter called parameters) of a plurality of optical elements.
Therefore, in consideration of the aforementioned points, the present invention has as its object to provide an optical apparatus and an adjustment method thereof whereby, even in the case in which the parameters of the optical elements to be adjusted have mutually dependent nonlinear correlations among a plurality of optical elements, better functions and higher performance than in the prior art can be obtained using optical elements of less-than-conventional precision, automatically and without the skilled technicians conventionally required. A further object of the present invention is to provide a method of ameliorating the decrease in functions and performance of optical apparatus arising from the movement or transportation of an optical apparatus or from changes over time or the like.
In order to achieve the aforementioned objects, the optical apparatus of the present invention is an optical apparatus having an adjustment apparatus and an optical unit comprising a plurality of optical elements, the adjustment apparatus sequentially providing control signals that, according to a probabilistic search technique, change the parameters of a stipulated plurality of optical elements among the optical elements to become parameters that cause functions of the optical apparatus to satisfy stipulated specifications.
Moreover, the optical apparatus adjustment method of the present invention is an optical apparatus adjustment method that controls a plurality of optical elements constituting an optical unit, comprising the steps of sequentially providing control signals that, according to a probabilistic search technique, change parameters of a specific plurality of optical elements among the optical elements, and searching for optimal values at which functions of the optical apparatus satisfy stipulated specifications.
By means of this optical apparatus and adjustment method therefor, a specific plurality of optical elements among a plurality of optical elements of an optical apparatus that affect a stipulated function consists of optical elements that change their element parameters depending on values indicated by the control signal, and the values of the plurality of control signals given to this specific plurality of optical elements are changed by the adjustment apparatus according to a probabilistic search technique so that the functions of the optical apparatus satisfy stipulated specifications, so in the event that adjustment of the parameters of the optical elements that effect the stipulated function becomes necessary, better functions and higher performance than in the prior art can be obtained automatically and without the skilled technicians conventionally required. Moreover, it is also possible to ameliorate the decrease in functions and performance of optical apparatus arising from the movement or transportation of an optical apparatus or from changes over time or the like.
Here, the performance of an optical apparatus can be represented by a function F which takes arguments of the individual parameters of the plurality of optical elements provided in that optical apparatus that can be adjusted. To have the functions of an optical apparatus satisfy stipulated specifications is equivalent to finding the optimum solution to the function F. The present inventors took note of this point and discovered that genetic algorithms and other probabilistic search techniques are applicable to the adjustment of an optical apparatus.
Genetic algorithms are one type of probabilistic search technique and are algorithms that (1) act effectively in wide-area searches, (2) do not require differential values or other derived information outside the function F to be evaluated, and also (3) are readily implemented. Therefore, in the present invention, a genetic algorithm may also be used to change the values of the plurality of control signals with the aforementioned adjustment apparatus.
In addition, in the event that the aforementioned function F to be evaluated satisfies special conditions, by replacing the genetic algorithm with the simulated annealing method, which is also a probabilistic search technique, it is possible to improve the search efficiency. Therefore, in the present invention, the simulated annealing method may also be used to change the values of the plurality of control signals with the aforementioned adjustment apparatus. Thereby, while the performance obtained by adjustment is lower compared to that of a genetic algorithm, the adjustment time can be shortened.
Moreover, at the time that the adjustment apparatus is searching for optimal values, it is possible to use an evaluation function that performs weighted sum of a plurality of evaluation results of said optical apparatus.
In addition, in the present invention, it is possible to measure the parameter values while the parameters of the optical elements are being adjusted based on control signals, store them in memory paired with the observed value of the light output, and take the pair of element parameter values that give the largest evaluation value among the pairs as a local maximum. Thereby, it is possible to improve the search efficiency and greatly reduce the adjustment time.
Furthermore, the optical apparatus of this invention described above may be a laser.
Moreover, the optical apparatus of this invention described above may use deformable mirrors, or may be a wave-front controller. Furthermore, it may be a telescope.
Furthermore, the aforementioned adjustment apparatus in the optical apparatus and optical apparatus adjustment method described above may consist of an electronic computer, and thereby, the process of searching for a plurality of device parameters according to probabilistic search techniques so that the functions of an optical apparatus satisfy the stipulated specifications can be performed easily and reliably in a short amount of time.
Moreover, the storage medium of the present invention is characterized in that it stores a processing program executed by the electronic computer that searches for a plurality of device parameters according to probabilistic search techniques so that the functions of an optical apparatus satisfy the stipulated specifications.
By means of this storage medium, it is possible to store and save a processing program executed by an electronic computer for the optical apparatus of the present invention and the optical apparatus adjustment method of the present invention, so the adjustment of the optical apparatus can be performed at any location.
The other objects and other characteristics of this invention will be further clarified in the following detailed description based on the appended drawings.